000
ACUS11 KWNS 030824
SWOMCD
SPC MCD 030823
TXZ000-031100-
MESOSCALE DISCUSSION 1863
NWS STORM PREDICTION CENTER NORMAN OK
0223 AM CST SAT DEC 03 2016
AREAS AFFECTED...PORTIONS OF THE IMMEDIATE UPPER TEXAS COAST
CONCERNING...SEVERE POTENTIAL...WATCH UNLIKELY
VALID 030823Z - 031100Z
PROBABILITY OF WATCH ISSUANCE...20 PERCENT
SUMMARY...A CONDITIONAL RISK EXISTS FOR SURFACE-BASED SUPERCELLS TO
AFFECT THE IMMEDIATE COASTAL AREAS BETWEEN MATAGORDA AND CHAMBERS
COUNTIES...AND A TORNADO CANNOT BE RULED OUT FOR ANY WELL-ORGANIZED
STORM-SCALE CIRCULATIONS THAT CAN REACH THE SHORE. DUE TO THE
CONDITIONALITY AND LIMITED SPATIAL EXTENT OF THE THREAT AREA...A
WATCH APPEARS UNLIKELY AT THIS TIME.
DISCUSSION...SURFACE MESOANALYSES SHOWS A SLOW-MOVING WARM FRONT
FROM ZAPATA...BROOKS AND NORTHERN KENEDY COUNTIES NORTHEASTWARD...
OFFSHORE BUT VERY CLOSE TO THE COAST BETWEEN NORTH PADRE ISLAND AND
THE BRAZORIA COUNTY COASTAL WATERS...THEN GENTLY ARCHING EASTWARD
FROM THERE AT AN OBLIQUELY OFFSHORE ANGLE WITH RESPECT TO THE
GALVESTON AREA. THIS BOUNDARY IS FORECAST TO DRIFT NORTHWARD
THROUGH THE REMAINING PRE-DAWN HOURS...IMPAIRED SOMEWHAT BY
CONVECTIVELY PRECIP-RELATED REINFORCEMENT OF STATIC STABILITY AND
BAROCLINICITY TO ITS NORTH. HGX RADAR IMAGERY CONSISTENTLY HAS
SHOWN EPISODIC MESOCYCLONES WITHIN A CLUSTER OF CONVECTION LOCATED
OFFSHORE FROM BRAZORIA...GALVESTON AND CHAMBERS COUNTIES...ALONG AND
NORTH OF THE VORTICITY-LADEN SURFACE FRONTAL ZONE.
GIVEN ITS LOCATION IN THE STABLE AIR...WITH EAST-NORTHEAST SURFACE
WINDS AND TEMPS IN THE 60S F...THE VERY LARGE HODOGRAPHS OF THE HGX
VWP QUITE LIKELY OVERSTATE THE ACTUAL SRH AVAILABLE TO SURFACE-BASED
CONVECTION INTERACTING WITH THE FRONT. NONETHELESS...0-1 KM SRH
200-400 J/KG IS POSSIBLE ALONG THE UPPER TEXAS COAST FRONTAL
SEGMENT...WHERE IT UNDERLIES A DEEP...35-40-KT...SOUTHEASTERLY TO
SOUTHERLY LLJ. THE LLJ SHOULD BE MAINTAINED THROUGH AT LEAST
MIDMORNING WITHIN A BROAD WARM-ADVECTION ZONE...IN TURN RELATED TO
MASS RESPONSE AHEAD OF A SLOW-MOVING UPPER CYCLONE OVER NORTHERN
MEXICO. ROUGHLY 50 KT EFFECTIVE-SHEAR MAGNITUDES ALSO SHOULD BE
MAINTAINED OVER THE AREA GIVEN ESSENTIALLY STEADY-STATE
MID/UPPER-LEVEL FLOW. THOUGH MOST OF THE SURFACE-BASED CONVECTION
SHOULD REMAIN OVER THE GULF...THAT MASS RESPONSE MAY ALLOW A SLIVER
OF FAVORABLE WARM-SECTOR AIR (WITH MLCAPE AROUND 500-800 J/KG) TO
REACH THE COAST BENEATH THE LLJ...ACCOMPANIED BY A MARGINAL TORNADO
RISK.
..EDWARDS.. 12/03/2016
...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...
ATTN...WFO...LCH...HGX...
LAT...LON 28639602 28949561 29529497 29699445 29619430 29579429
29419464 29369471 29319471 29119507 29039513 28819548
28679578 28639602